1,8 channel-64 sims gsm gateway 2,IMEI change automatically 3,Call ... Ringing voltage 75V, Call connected voltage 9-12V Dialing tone Frequency 420Hz, Busy-Toneand Disconnect Tonewith 0.35secon/off DTMF ON ... 100ms, Picking current 23mA/43mA 25HzRing,600 ohm Impedance 8 channel--64 sim cards gsm gateway